1. Field of Invention
This invention relates to a device and method for recording data on a write-once or rewritable optical disk, particularly to recording power conditions used therein.
2. Description of the Related Art
The Blu-ray Disc (BD; registered trademark) is known as a new standard for optical disks. With a BD, a standard-speed BD-RE has been gaining practical use in recent years as a rewritable type of optical disk. The one-side capacity of a BD-RE is 25 GB with a single layer, and 50 GB with two layers. A BD-R is also under development as a write-once type of optical disk.
The following method for recording data on an optical disk is known for a conventional BD (see FIG. 11). The upper part in FIG. 11 is an example 900 of digital data (hereinafter referred to as recording data) to be recorded on an optical disk. The recording data 900 includes a high-level (Hi) signal with a pulse width of 2T (2 times the recording clock period T), a low-level (Lo) signal with a pulse width of 5T, and a Hi signal with a pulse width of 8T, in that order. The middle part in FIG. 11 is an example 901 of a recording pulse produced according to the recording data 900. The level of the recording pulse 901 corresponds to the power of the laser beam to be directed at the optical disk. The lower part in FIG. 11 shows a recording state 902 of a recording track 903 of the optical disk. This recording track 903 is irradiated with the laser beam at power levels corresponding to the recording pulse 901. The mark 904 is formed at a portion of the recording track 903 irradiated with the laser beam at a power level of at least a predetermined lower limit, and the space 905 is formed at a portion irradiated with the laser beam at a power level below the lower limit. In the example in FIG. 11, the boundary between the mark 904 and the space 905 corresponds to a change point in the levels of the recording data 900.
The recording pulse 901 generally includes a top pulse 907, a multi-pulse 909, a cooling pulse 910, and a space pulse (see FIG. 11). The level of the top pulse 907 is a peak level 906. The levels of the pulses of the multi-pulse 909 are switched binarily to the peak level 906 and a bottom level 908. The level of the cooling pulse 910 is equal to the bottom level 908. The space pulse is equivalent to a bias level 911 maintained from the rear end of the cooling pulse 910 to the front end of the next top pulse 907. The peak power of the laser beam corresponding to the peak level 906 is higher than the lower limit of the power required to form a mark on the recording track 903, and the bottom power of the laser beam corresponding to the bottom level 908 is lower than the lower limit. Furthermore, the bias power of the laser beam corresponding to the bias level 911 is lower than the above-mentioned lower limit and higher than the bottom power. The mark 904 is formed at the portion of the recording track 903 irradiated with the laser beam at a power corresponding to the top pulse 907 and the, multi-pulse 909, and the space 905 is formed at the portion irradiated with the laser beam at a power corresponding to the bias power. The length of the mark 904 here is determined by whether or not there is a multi-pulse 909 and by the number of pulses included therein. Such conditions regarding the waveform of the recording pulse 901 are generally called a write strategy. Write strategies are broadly classified into recording power conditions and recording pulse conditions. Recording power conditions specify the peak power, bottom power, and bias power. Recording pulse conditions specify the temporal conditions for the top pulse 907, the multi-pulse 909, and the cooling pulse 910 (such as their pulse widths and edge positions). Marks can be formed in right shapes particularly by suitably setting the write strategy.